Safety Performance of Rural Offset-T Intersections

Abstract

Offset-T intersections represent a special geometric configuration where two three-leg intersections adjoin the major road from opposite directions within a short separation distance. The prevalence of offset-T intersections in rural areas coupled with the lack of research evaluating their safety performance led to the development of a series of safety performance functions for rural stop-controlled intersections that considered the effects of the offset direction and separation distance. In addition, crash modification factors (CMFs) were developed to estimate the change in crash frequency associated with converting a rural offset-T intersection into a conventional four-leg intersection. A series of mixed-effect negative binomial models for crash occurrence was generated based on 10 years of crash data from a sample of 299 offset-T intersections and 301 four-leg intersections with minor stop control along rural two-lane highways in Michigan. Compared with conventional four-leg intersections, offset-T intersections exhibited 35% more crashes regardless of the offset distance or direction. Considering crash types, single motor vehicle crashes occurred more frequently at offset-T intersections, and increased as the offset distance increased. Rear-end crashes also occurred more frequently at offset-T intersections, with left offsets having greater crash occurrence than right offsets. However, angle crashes were 40%–69% lower at offset-T intersections because of the elimination of the direct crossing maneuver. Considering the ranges of offset distance and direction utilized within this study, the total (non-animal) CMF for converting an offset-T into a four-leg intersection was 0.74.